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SCEC2023 Plenary Talk, Earthquake Geology

Looking beyond the Great Southern California Shakeout: The February 06, 2023 Kahramanmaraş earthquake sequence reminds us to expect the unexpected

Sinan O. Akciz, & Cengiz Zabcı

Oral Presentation

2023 SCEC Annual Meeting, SCEC Contribution #13299
The 6 February 2023 Kahramanmaraş earthquake sequence generated significant shaking and damage throughout southeastern Turkey and Syria, a region known for its historical large earthquakes. The sequence started with an Mw7.0 on a 20-km long secondary fault called Narli fault and initiated the Mw 7.8 Pazarcık earthquake along the tectonic boundary between the Anatolian and Arabian plates, rupturing it bilaterally for over 300 km. These earthquakes occurred in a known seismic gap with a long recurrence time of historical earthquakes. Maximum slip measurements of ~7m were made in the field close to the junction of the main rupture with the Narli fault. Farther to the NE, the slip decreases to a mean value of ~3 m, but then it increases again to ~6.5 m at Kurucaova village. Slip drops to less than a meter to the NE of Celikhan and diminishes to the N of the Karaköse village. This leaves an 18 km-long unbroken fault piece at the surface until the SW-termination of the 2020 Mw 6.8 Sivrice Earthquake rupture. The Mw7.8 earthquake increased stress along the E-W oriented sinistral Çardak Fault, where the Mw 7.6 Ekinözü earthquake occurred 9 hours later, rupturing ~ 140 km bilaterally. Maximum slip measurements of ~8.5 m were measured just east of the epicenter. The slip tapers to 2.5m to the east before establishing a path along a new fault parallel to the East Anatolian Fault (EAF). Slip along the 40km-long fault zone is about 1 m, with maximum sinistral slip reaching ~2.5 m.

The North Anatolian fault is a close analog of the San Andreas fault in California, with the two continental transforms sharing similar slip rates and total length. But the Kahramanmaraş earthquake sequence reminds us that: (1) slow-slipping faults, such as the EAF, can produce earthquakes that are larger than historical earthquakes; (2) earthquakes along faults with even lower slip rates and longer recurrence intervals may initiate larger magnitude earthquakes along nearby mature faults; (3) increased stress along faults with even lower slip rates can trigger large magnitude earthquakes within hours of the main earthquake and increase the damaged region significantly, impacting crucial rescue efforts. As SCEC community, many of these observations and their implications may be new. Still, it is perhaps the right time to increase the awareness of California residents and public employees on seismic hazards beyond the Great California Shakeout and the HayWired scenario earthquakes.